A document scanner is a device which converts a visible image such as a photograph, transparency or printed paper into an electronic form suitable for copying, storing or processing by a computer. Document scanners typically have a controlled source of light which is reflected off the surface of a document or is transmitted through a transparent document onto an array of photosensitive devices. The photosensitive devices convert received light intensity into an electronic signal. In some configurations, the light source is a long tube providing a narrow band of light which extends to each edge of one dimension of the document or beyond the edges.
For electric discharge lamps such as fluorescent bulbs, the color balance of the light varies depending on the temperature of the bulb. When such a light source is first powered on, color balance of the light varies dynamically along the length of the bulb until the overall temperature of the light source stabilizes. Moreover, during long scans, the temperature of the bulb can change enough to cause an unsatisfactory shift in the bulb color balance causing a color shift in the image scanned.
One solution to this problem is to leave the bulb on continuously, which allows the bulb temperature to reach a steady state. This solution is a costly solution due to frequent changing of the light source and continual power usage.
Thus, the need exists for a scanner method and apparatus that will compensate for color variances of the light source as a function of temperature in a dynamic manner, for example during each and every document scan, to thereby allow document scanning to begin within a second or two after the light source has been initially energized.